1. Field of the Invention
The present invention relates to an impeller for a fluid transmitting device, such as a pump impeller and a turbine impeller, comprising: a hub; a bowl-shaped shell connected to an outer peripheral portion of the hub via an annular weld seam; and a plurality of blades rising from an inner peripheral surface of the shell.
2. Description of the Related Art
Such an impeller for a fluid transmitting device is known from, for example, Japanese Patent Application Laid-open No. 2001-108059.
In such a conventional impeller for a fluid transmitting device, MIG welding and TIG welding are widely performed to weld a hub to a shell. However, MIG welding requires a process for removing spatter produced from a work in the welding; and both MIG and TIG welding requires a large amount of heat input for welding the entire periphery of the hub and the shell, so that thermal distortion is often generated in the work, and in this case, a distortion removing process is required. Further, a skill is required for visual inspection as to whether the weld seam is good or not.
Also, Japanese Patent Application Laid-open No. 2003-214523 discloses a method of manufacturing an impeller for a fluid transmitting device in which plural blades are annularly arranged on an inner surface of a bowl-shaped shell; an annular retainer plate for retaining radially inner ends of the blades is temporarily fixed by welding on the inner surface of the shell; after the temporary fixation, the blades and retainer plate are brazed to the inner surface of the shell; and after the brazing, a hub is welded to the central portion of the shell.
However, in the conventional method of manufacturing an impeller for a fluid transmitting device, spot welding or projection welding is typically performed to temporally fix the retainer plate on the inner surface of the shell. In either welding, the shell and the retainer plate are required to be strongly pressed to each other, and the resultant pressure may cause distortion in the shell and the retainer plate. Particularly in the projection welding, deformation of a protrusion which is formed on one of opposed surfaces of the shell and the retainer plate, is likely to spread to the surrounding to cause distortion there.